edited

Problem

For 64-bit clean functionality, convenience, and symmetry, the Big MPI principles being applied in Ticket #80 to collective operations should be applied to MPI point-to-point functionality.

Proposal

MPI needs to be 64-bit clean throughout.

Changes to the Text

MPI_Count will replace int for counts; support counts > 2^31

Other checks of any non-64-bit-clean features in point-to-point after review.

This ticket does not address the MPI_Rank issue; that is a separate, cross-cutting ticket.

Impact on Implementations

No current API is impacted. New _X APIs for all point-to-point operations affected will be needed.

MPI implementations will have to be 64-bit clean inside since count*extent > 2^31 is already problematic for some implementations. New APIs will have to be added and the internals of MPI will have to be 64-bit capable for buffers and related issues.

Impact on Users

Users who opt in with the new API will be able to send and receive larger messages [MPI_Count]